Nanoparticles for hydrogen storage, transportation, and distribution

ABSTRACT

This invention uses nanoparticles to broaden the range of economic materials, improve performance across this broader range, and thereby lower costs of hydride and other storage systems. Nanoparticles can have dramatically different mechanical, chemical, electrical, thermodynamic, and/or other properties than their parent (precursor) materials. Because of this fundamental characteristic, nanophase materials can greatly improve the range of possibilities of materials selection, performance, cost, and practicality for hydride storage systems, advancing the early commerciality of such systems for hydrogen fuel cells or other applications. Among such hydrogen storage improvements are cheaper and better-performing metals, alloys, and/or compounds; lower weight; and reduced storage volumes.

This application claims benefit of U.S. provisional patent applicationserial No. 60/151,973 filed on Sep. 1, 1999.

FIELD OF THE INVENTION

This invention relates to the storage, transportation, and distributionof hydrogen and other low density fuels using nanoparticles.

BACKGROUND OF THE INVENTION

Hydrogen for use in fuel cells (and possibly as a fuel in internalcombustion engines) appears poised potentially as the next majorevolution in energy usage. Unfortunately, safely storing hydrogen andother low molecular weight fuels is currently very difficult andexpensive. Such fuels are now stored in pressurized tanks or in hydridestorage systems. Hydride storage is far safer than compressed hydrogengas storage, and safer even than gasoline on an equivalent-energy basis(Reilly, J. J. Sci. Amer. 1980, 242(2), 2). However, hydrides carry bothweight and cost penalties versus compressed hydrogen. As anotheralternative, hydrogen can be created as needed by reformers, butefficiencies are reduced. Hydrogen vehicle systems' space and weightpenalties versus gasoline are about 5 times the space if stored ascompressed gas, or still 3 times the space plus between 40 to 470 extrapounds of weight if stored as a metal hydride, even after taking intoaccount the greater efficiency of hydrogen fuel cells (HFCs) versusgasoline internal combustion engines (ICEs). Additionally, these spacelimitations require storage to be closer to passengers, compoundingsafety concerns.

These storage limitations penalize not just on-board vehicle storage andvehicle range, but also the capacity for overall transportation anddistribution of hydrogen versus gasoline or other existing fuels, andits storage prior to use. These limitations in turn limit where, howefficiently, and how cleanly hydrogen can be produced. For example,hydrogen generation onboard vehicles from methanol or gasoline reformerscuts total emissions only 7-35%, while steam reforming at servicestations would reduce emissions by 40%, and remote generation wouldreduce emissions by 60-70%, given a practical and economical storagemethod. A better method of both on-board storing, and transporting anddistributing, of hydrogen, including pure HFC vehicles would have asignificant and broad positive impact on this emerging new industry.

Generation of hydrogen at the site of remote electric power generatingplants and then shipment of the hydrogen to markets using economicalstorage systems could entail less energy loss than if electricity istransmitted to local service stations for generating hydrogen on site.Cheaper natural gas costs could also be accessed by generating hydrogencloser to the sources of gas. Economies of scale of larger volumehydrogen production could be realized. Transmission-distribution wiresin many cases could be avoided. And attendant air pollution could beremoved from the local area urban centers, where smog is the principalconcern. Renewable energy supplies (solar, wind, etc.) could also beaccessed given an economic transportation system.

Stationary HFCs are likely to be introduced in homes and industryconcurrently with vehicular use. Because manufacturing costs of HFCs andhydrogen generators will both decline with the volume permitted byintroduction of HFCs to the vehicle market, HFCs should simultaneouslybegin penetrating homes and industry, for both heating and electricity.Whereas the proton exchange membrane (PEM) HFC is targeted for vehicles,with an efficiency of about 50% versus 25% for the ICE vehicle, stillhigher-efficiency fuel cells are being developed for stationary use,with efficiencies of 60-80%, versus 30-60% for conventional powergeneration (the upper ends of ranges in both cases includingcogeneration). These stationary fuel cells include the molten carbonate,phosphoric acid, solid oxide, alkaline, direct methanol, and other fuelcells.

HFCs for portable power products, such as, but not limited to computers,can be introduced concurrently with vehicular use; again, riding thecost and technology curves developed for HFCs and hydrogen generationfor the other markets. These stationary HFC markets, portable powerproduct markets, and vehicle HFCs will all require hydrogen to besafely, inexpensively, and conveniently delivered, as well as storedbefore use.

HFC's main problems are vehicle range, safety, and hydrogen fuelavailability. These problems are all in turn aspects of the problem ofhydrogen storage. A HFC system may achieve the same range as forgasoline ICE (a usual target being 380 miles), but 3-5 times the spaceand possibly far greater weight are required compared to gasoline. Theextra space required also adds to real or perceived safety concerns.These space and weight penalties also affect the ease of transportationand distribution of hydrogen, which in turn makes vehicle range concernsstill more sensitive. The space and weight limits, and associated safetyconcerns, represent the largest negatives for HFCs.

Most critical is the space required for compressed hydrogen storage.Hydrogen today is stored at 2,000-2,500 psi (14-17 mPa) and requireslarge, heavy containers. Even at 5,000 psi, the standard currently beingpursued for development in the auto industry, the space required isstill about 5 times that of gasoline, even after allowing for thegreater efficiency of the HFC versus the ICE. Table 1 summarizes theselimits, along with weight limitations of the various systems.

This greater space requirement either limits the vehicle's range betweenrefueling—especially important with a limited hydrogeninfrastructure—and/or requires storage closer to passengers, raisingsafety concerns.

TABLE 1 Space and Weight of Fuel and Tanks for 380 Mile/Tank RangeVehicle 5000 Psi Gasoline Hydrogen Hydride Mileage 29 mpg 64 mpg (2.2times 64 mpg (2.2 times gasoline ICE) gasoline ICE) Gallons 13 gallons4.7 kilograms 4.7 kilograms Tank Size 14 gallons Volume 1.87 cubic ft.9.36 cubic ft. 5.7 cubic ft. Volume versus — 5 times 3 times GasolineWeight Fuel 73 lbs. 10.3 lbs. 10.3 lbs. Weight Tank 29 lbs. 100 lbs.140-570 lbs.* Total Weight 102 lbs. 110 lbs. 150-580 lbs.* Weight versus— Similar +40-470 lbs.* Gasoline *Lower weight is magnesium hydride;higher weight is more economical and currently practical iron-titaniumhydride.

Source: “Onboard Compressed Hydrogen Storage,” by Brian James, C. E.Thomas, and Franklin D. Lomax, Jr., Directed Technologies, Inc,Arlington, Va., February 1999.

If hydrogen gas were compressed to 10,000 psi (also being considered fordevelopment), it would occupy about the same space as liquid hydrogen;but this is still about 3 times that of gasoline. However, evenpressurizing to 5,000 psi may raise some significant safety concerns,and pressuring to 10,000 psi, when and if economically possible, mightsimply add to those concerns. Liquid cryogenic hydrogen storage requiresvery low temperature of −253° C.

Liquid cryogenic hydrogen, which takes up 3 times the space thangasoline, is impractical due to the extremely low temperatures required(minus 423 degrees Fahrenheit), the energy and cost that must beexpended to liquefy hydrogen (approximately doubling its deliveredcost), and the losses during storage as the liquid hydrogen slowly boilsoff and escapes. Some such losses might also occur in 10,000 psicompressed hydrogen gas.

Hydrogen has many safety concerns. Hydrogen must in any case becompressed to a significant pressure, since uncompressed hydrogen (i.e., at atmospheric pressure) has only 1/1330 the energy density, and thustakes 1330 times the space, of gasoline. The onboard vehicular storageof hydrogen gas at any pressure raises safety concerns in the event ofan accident, since the storage tank must be far stronger than that forgasoline to prevent rupture. The sudden release of such highlycompressed gas could itself pose a significant safety hazard in theevent of an accident, spewing an instantly flammable cloud.

Slower leaks likewise pose an ongoing concern. This is especially truesince parking indoors would create its own safety problems, which wouldrequire re-engineering buildings. This is because hydrogen rises, andmost garages are not protected from upward rising gasses. Many bedroomsand most living spaces are built over the garage in current housingdesigns. The slow boiloff of very high pressure 10,000 psi gas(mentioned above) could be hazardous.

To accommodate the extra required space, compressed hydrogen fuel tanksmay have to extend either under the vehicle floorboards or in overheadroof areas, placing the fuel closer to passengers. Locating hydrogentanks closer to passengers appears even riskier than for gasoline tanks.

Carbon fiber-reinforced plastic compressed hydrogen fuel tanks willimprove. However the few occasional inevitable accidents (including somethat have already occurred) could cause continuing safety concerns forcompressed natural gas onboard vehicles under extreme pressures,especially since hydrogen already has a (largely undeserved) safetyimage problem.

To counter the need for onboard storage of hydrogen and thus eliminatealtogether such safety concerns, and perhaps even more importantly, toprovide greater availability of hydrogen fuel supplies during earlyyears of introduction, auto companies are considering alternatives topure HFCs which have onboard hydrogen reformers. These onboard reformersmanufacture the hydrogen only as it is actually used in the fuel cell,thus eliminating storage and safety concerns. These reformers typicallyuse methanol or gasoline fuel, thus reducing or eliminating fuelavailability concerns. However, these reformers are inferior to purehydrogen HFCs by virtually all other measures: emissions reductions,cost of fuel per mile, cost of vehicle, and oil import reductions.

Hydrogen storage as a hydride virtually eliminates the safety penalty aswell as much of the space penalty of compressed gas storage versusgasoline; however, the tradeoff is weight and cost penalties. Stored asa compressed gas, hydrogen is on parity in weight with gasoline, asshown in Table 1. Hydrogen on an energy basis weighs only one third ofgasoline. This reduces to about one seventh the weight of gasolinerequired in a vehicle after allowing for the estimated 2.2 times greaterefficiency of the HFC versus the ICE vehicle. However, with the extraweight of the tank, compressed hydrogen storage still weighs about thesame (Table 1). Light-weight 5,000 psi carbon fiber-wrapped compressedgas storage systems under development, which will store up to 10% ofhydrogen by weight, will make this approximate weight parity possible.

Thus, as Table 1 shows, a 14 gallon gasoline tank, holding 13 usablegallons and capable of traveling 380 miles at 29 miles per gallon, wouldweigh about 102 pounds: 73 pounds of gasoline and 29 pounds of tank andrelated equipment. A 4.7 kg. compressed hydrogen storage system capableof the same range would weigh about the same, 110 pounds: including 10.3pounds of hydrogen and 100 pounds of tank and related equipment. In thiscompressed gas form the limitation is not weight, but rather the verysignificant 5 times greater space, and accompanying safety concerns.

Hydrogen also faces transportation, distribution and storage problemsprior to use. Transportation via tank truck of either liquid hydrogen orhighly compressed (up to 10,000 psi) hydrogen is possible. However,trucking of liquid hydrogen would not be economic for widespread HFCvehicle use due to the higher costs of liquefaction, and trucking ofcompressed hydrogen gas would, as of now, raise problems of both safetyand economic cost. Pipelines are prone to hydrogen embrittlement, and inany case, a network does not now exist for distribution of hydrogeneither to service stations or to homes or industry.

The answer now being considered is on-site service station generation ofhydrogen, either by steam methane reforming or by electrolysis. However,electrolysis is only an initial, interim solution, and on-site steammethane reforming adds to the local-area smog pollution, reducing someof the smog-abating benefits of HFCs.

Remote-site steam methane reformers would reduce the local-area smogpollution of HFCs to virtually zero, making them more substantialcontributors to clean air in urban centers, where smog is the majorconcern. Remotely sited steam methane reforms could also be larger,giving greater economies of scale and cheaper costs of manufacturinghydrogen—if an economical means existed to transport such hydrogen tothe point of use.

If steam methane generation or electrolysis on site at the servicestation is used, a practical means of hydrogen storage would enablethese reformers or electrolyzers to operate “steady state,” including atnight when the service station is closed. This method appears moreeconomic than the other choice to “follow load” of traffic flow.

Hydrogen can be reformed as needed from other chemicals (e.g., methanol,gasoline, or hydrocarbons) that are easier to store than hydrogen andcan take advantage of existing distribution systems. However,inefficiencies, poisons, and environmental penalties partly offset thesebenefits.

Natural gas and other light-density fuels face the same storage problemsas hydrogen, and could likewise benefit from a more practical means ofstorage.

Hydrogen storage methods considered above include physical storage in acompressed gas or liquefied state, and solid-state storage usinggas-on-solid adsorption in materials such as, but not limited to highsurface area carbon.

Activated carbon or activated charcoal is usually used for gas-on-solidsadsorption. This technology works better at low temperatures. Theequipment and cost of maintaining low temperatures complicate use ofthis technology, especially in vehicles.

Solid-state storage, gas-on-solids and metal hydrides are options whichare safer technologies and they provide high storage capacity thanphysical storage systems. They are more expensive and heavier. Currentresearch is aiming to determine the hydrogen adsorption/desorptionproperties of commercially available carbons and zeolites. Solid statestorage capacities, rates of charge and discharge, thermal andmechanical effects and costs of available materials are important costand operating parameters for hydrogen storage systems.

With gas-on-solids adsorption technology, hydrogen can be stored bybeing adsorbed onto the surface of activated carbon. This technologyprovides better volume density than compressed gas storage. The weightand volume densities of this application are comparable to liquidhydrogen systems. In a main drawback, the adsorption of hydrogen oncarbon requires maintaining a temperature below 150 K (−190° F.).

A metal hydride form of hydrogen storage would reduce hydrogen's spacepenalty versus gasoline from fivefold to about threefold, even beforeconsidering greater vehicle design efficiencies. Even more important,storage as a metal hydride would virtually eliminate safety concerns ofhydrogen storage, to even less than for gasoline. This greatly increasedsafety would in turn permit storage closer to passengers, thus forpractical purposes in totally new vehicle designs perhaps eliminatingthe space limitation altogether. Seen in this light, safety concerns maybe the principal reason for space limitations of compressed gas storage.

However, metal hydride systems would add 40-470 pounds more weight thangasoline (on a total system basis), depending on which of a wide rangeof hydride metals is used. The cost of these metals may also besignificantly greater than for a carbon fiber wrapped compressedhydrogen storage tank. These weight and price penalties of hydrideshave, unfortunately, more than offset their safety and volume benefitsin auto engineering thinking to date.

With metal hydride technology, certain metals, alloys and othermaterials can be used to absorb and retain hydrogen under specifictemperature and pressure conditions. They release hydrogen underdifferent conditions. These metals are called metal hydrides whencontaining hydrogen. Magnesium hydrides are popular because magnesium isa relatively cheap and abundant metal and can absorb large amounts ofhydrogen for its weight. Hydrides are safe and a have very high hydrogenvolumetric storage capacity as compared with other methods of hydrogenstorage. Unfortunately, metal hydrides are currently expensive.Currently, lower cost hydride materials require high temperatures torelease hydrogen. On the other hand, hydrides which release hydrogen atlower temperatures are expensive and have less storage capacity.

A typical hydride storage system can contain several forms hydrogen atits different charging, storage, and discharging stages. A solidsolution of hydrogen atoms can exist in a metal lattice or coexist withthe monohydride phase of the hydride (e.g., XH, where X is ahydride-forming metal or other element). A monohydride phase can existalone. Both monohydride phase and dihydride phases (e.g., XH₂) cancoexist. A dihydride phase can exist alone. See, E. Wiberg and E.Amberger, Hydrides of the Elements of Main Groups I-IV, Elsevier, 1971,pp. 1-12. These storage mechanisms are usually different at ahydrogen-binding material's surface and in its bulk.

Hydrogen reacts with many elements to form compounds. Of these, thetransition metals (Groups IIIA through VIIIA in the periodic table,including the lanthanides and actinides) are most important because theycan absorb large quantities of hydrogen and form metallic hydrides.Metallic hydrides exhibit the general properties of metals, i.e., highelectrical and thermal conductivity, hardness, and metallic luster.Typically hydrides are powders with average diameters of a few microns.

There are many hydride-forming materials. The terms hydride materialsand hydride-forming materials are used interchangeably in thisapplication and in many references. New alloys and other materials willallow even better hydride properties. Currently popular metal hydridesystems include alloy ratios of a first metal A, and a second metal B toform AB₅ (e.g., LaNi₅), AB (e.g., FeTi), A₂B (e.g., Mg₂Ni),and AB₂(e.g., ZrV₂). A few examples of currently used hydrides include:LaNi_(4.7)Al_(0.3), Ti_(0.98)Zr_(0.02)V_(0.45)Fe_(0.1)Cr_(0.05)Mn_(1.4),Ca_(0.2)M_(0.8)Ni₅ (wherein M represents mischmetal), CaNi₅, Ni₆₄Zr₃₆,Fe_(0.8)Ni_(0.2)Ti, FeTi, Fe_(0.9)Mn_(0.1)Ti, CaNi₅, LaNi₅,LaNi_(4.7)Al_(0.3), Mg₂Ni, Mg₂Cu, Mg, V, Ti, Zr, Th, Pd, Ca, and Li. Asmall percentage of another metal can be added to the alloy to affectperformance. Other hydrides include non-reversible chemical hydridessuch as, but not limited to LiH_(x), AlH, NaH, and B₂H₄. Liquid organichydrides include chemicals such as, but not limited to decaline, andmethyl cyclohexane used with a catalyst at 200° C. Mischmetal is analloy of rare earth metals containing about 50% lanthanum, neodymium,and similar elements.

The equilibrium pressure-composition-temperature relationships of ametal/hydrogen system can be conveniently summarized by a P-C isothermof which an idealized version is showed in FIG. 1. Hydrogen gas pressureis plotted versus the ratio of hydride:metal. The label C can be theconcentration of hydrogen or the ratio of hydrogen to metal. The P-Ccurve shows three distinct sections. Initially the isotherm ascends fast(section A-B) as hydrogen enters the metal lattice and occupiesinterstitial positions. At low concentrations of hydrogen, thecomposition/pressure relationship is ideal and obeys Sievert's Law:

H/M=K _(s) P ^(½)  (Equation 1)

where H/M is the hydrogen to metal ratio, K_(s) is Sievert's constant,and P is the equilibrium hydrogen pressure. As the hydrogen content inthe metal increases, the hydrogen atoms interact (via the elasticstrains introduced in the metal lattice) and the pressure/compositionbehavior departs from this ideality. This is reflected by a decrease inthe slope of the isotherm. At a critical average hydrogen concentration,the metal/hydrogen system forms a new hydride phase (see area C₁ in FIG.1). There is a discontinuity in an increasing amount of hydrogen thatthe metal can store. The flat, or plateau region in the P-C isothermcorresponds to the co-existence of the metal and hydride phases. Toforce more hydrogen into the alloy requires increasing the external gaspressure. This is represented by the rapid increase in the C-D region ofthe P-C isotherm curve.

In general, the plateau pressure for hydrogen loading is different fromthat for unloading. This pressure difference is called hysteresis. Aflat plateau in the P-C curves is usually a required feature for gaseoushydrogen delivery systems to allow a large quantity of hydrogen can bestored reversibly at a constant pressure. It is important that theplateau be as wide as possible (large hydrogen storage capacity) andthat at room temperature the plateau pressure be close to atmosphericpressure, since the storage container does not need to be especiallystrong and can thus be of light weight. Equation 1 may be affected orfollowed more closely by using nanoparticular hydrides instead of bulkhydrides.

The palladium/hydrogen system has been studied extensively, beginningwith the early work of Graham well over a hundred years ago. Palladiumis an attractive material due to its ability to readily dissociatemolecular hydrogen to atomic hydrogen at its surface, but is overlyexpensive. Unfortunately, the direct replacement of palladium forcheaper metals or alloys is hindered because these metals form oxide orother layers and the reduced surface reaction limits the hydrogen fluxinto the metal.

To exploit the rapid bulk diffusion of hydrogen in the refractorymetals, a palladium can be coated on a less expensive material. Thisallows the dissociation of the molecular hydrogen by the surfacepalladium layer, transport through the refractory metal bulk, andfinally reassociation on the opposite surface.

In one example, the Group V metals are subject to embrittlement.However, the regime where this is a problem is well below roomtemperature. Should the surface palladium layer develop defects, thiswould not render the material useless since it would merely expose asmall area of the refractory metal. Composite metal materials, such as,but not limited to plating foils of Group V metals (e.g., vanadium) withthin layers of palladium, are known. While it is clear that viablecomposite metal materials in larger scales have been constructed,improvements of the process are still required to make these structuresmore efficient. Removal of the refractory metal surface oxide layer isimportant to ensure hydrogen flux into the metal. Various chemical andmechanical techniques have been used to achieve this, but most allowregrowth before coating with the top palladium or palladium alloy.Another concern is the quality of the palladium or alloy layer.

The hydriding reaction proceeds inwardly from the surface of the alloy(Reilly, J.; J. Sci. Amer. 242(2), 2, 6 (1980)). Cracks and fissures arecreated, increasing the surface area. However, this surface area isprobably still much lower than present in nanophase materials. Poroushydrides are described by Congdon in U.S. Pat. No. 5,443,616.

In the past several years nanophase materials, including metals andceramics, have begun being designed and manufactured. These havedramatically different characteristics than their precursor (parent)materials, making them act almost like new materials. These differentcharacteristics can be customized by controlling the size, as well asshape and crystalline character of the nanophase grains. For example,see Richard W. Siegel's review in “Creating Nanophase Materials,”Scientific American, December, 74-79 (1996).

Nanoparticles include atomic clusters, molecular clusters, agglomerates,micelles, and other particles with nanometer dimensions. Nanoparticlesare usually made by such techniques as chemical vapor deposition (CVD),physical vapor deposition (PVD), physical vapor synthesis (PVS),reactive sputtering, electrodeposition, laser pyrolysis, laser ablation,spray conversion, mechanical alloying, and sol gel techniques. New,lower cost methods are being evolved from these and similar means ofproduction. In general, nanoparticles can be synthesized from atomic ormolecular precursors or by chemical or physical means.

Many materials with some nanoscale feature (e.g., crystals or grains)are often confusingly called nanoparticles, whereas in fact they arelarger composite structures with some nanoparticle features. These largestructures should be called nanostructured materials, nanostructures, ornanomaterials. For example, Ovshinsky describes hydrides made ofnanocrystallites in U.S. Pat. No. 5,840,440. However, thesenanocrystallites only describe the size of the crystals making up thecontinuous hydride bulk structure. These crystallites integrally formthe bulk material. There are no separable nanoparticles in thesehydrides.

Two other examples use mechanical alloying by ball milling. Alloyingnanoscale particles by ball milling was studied by Holtz and Imam [J.Mater. Sci., 32 (1997) 2267]. However, the resulting product was pressedinto large pellets. Song describes agglomerates with isolated grains ofsubmicron Mg₂Ni hydrides created by ball milling [Song, Y. M., Int. J.Hydrogen Energy, 20(3) 221-227]. However, it appears that most of theisolated grains are components of larger particles or agglomerates asdepicted in his electron micrographs. Moreover, size of the particles ismeasured by lower resolution scanning electron microscopy, which depictsa macrostructure with small microfeatures, and Song does notdifferentiate between agglomerates, grains, and individual particles.

Singh, et. al. [J. Alloys and Compounds, 227 (1995) 63-68] describesmore extensive ball milling with smaller primary particles. However, hisTEM shows that the majority of these small primary particles arecombined into parts of larger aggregates. Due to the high energyimparted by mechanical alloying, the nanoparticles are fused togetherinto larger alloyed aggregates. Such extensive ball milling isexpensive.

Imamura, et al. [J. Less-Common Metals, 135 (1987) 277] describe makingsmall hydride particles by evaporating magnesium into an atmospherecontaining THF. This method can theoretically engineer a separation ofthe nanoparticle metals, but is not clearly demonstrated to do so inthis instance. Imamura only roughly estimates particle size based onsurface areas calculated by BET surface analysis. This assumes perfectspherically shaped particles with no surface roughness. Imamura did notknow the number of such particles in the sample, their packing, theirshapes, agglomerations, or their size distribution. Methods ofestimating average particle size distribution are not amenable toparticles this small because of numerous measurement problems. BET canbe used to measure pore sizes due to their surface area, but cannotmeasure particle sizes of loose powders. For these reasons BET isespecially not suited for measuring nanoparticles due to numerousmeasurement problems. Again, grain sizes or solvated solids within a THFmedium are described instead of discreet nanoparticles. This THF workdescribes metal particles held together by THF to form THF-impregnatedaggregates or wet agglomerates by an expensive vacuum process. Theprimary particles are not significantly separable into discretenanoparticles.

Carbon or graphite nanotubes are a nanomaterial that has beeninvestigated for hydrogen storage. Most nanotubes have a submicron wallthickness and sometimes a diameter. Critical dimension is the smallestdimension of an object. The length of nanotubes is usually approximatelya micrometer (micron). The smallest nanotube diameters are still muchlarger than interstitial sites in hydrides.

Carbon nanotubes trap hydrogen within the inside diameter of thenanotube or as gas-on-solid adsorption. In a big difference, hydrideschemically store hydrogen at least partly within their bulk withininterstitial sites between metal atoms.

Carbon nanotubes may have other drawbacks. They are expensive tomanufacture and especially to purify. They could potentially create anexplosion hazard in an oxygen environment. Also, they usually need to bekept at low temperatures in order to retain hydrogen.

Current hydrogen storage technology focuses on macroscale hydrides,carbon nanotubes, compressed hydrogen and cryogenic liquid hydrogen.Instead of just improving these existing systems, it would be beneficialto take an entirely different approach.

SUMMARY OF THE INVENTION

This invention stores fuels with nanoparticles that can at leastpartially chemically react with hydrogen or optionally other low densityfuels. In the preferred embodiment, relatively pure, alloyed orcomposite metal nanoparticles can at least partially react with hydrogengas to form essentially reversible hydrides. Nanoparticularhydride-forming materials of the present invention can broaden the rangeof economic materials, improve performance of them, and thereby lowerthe costs and improve the economics of hydride storage systems. For manyhydride materials, the high surface to volume ratio of nanophaseparticles enhances hydrogen absorption and desorption rates, reducesexternal energy (e.g., waste heat) required for hydrogen desorption,improves other performance characteristics, and reduces the hydrideweight and often volume per unit of stored hydrogen, thus bothbroadening the range of materials that can be used and enhancing theirperformance characteristics.

DETAILED DESCRIPTION

This invention relates to improving performance, cost, and range ofpossible materials, of hydride storage by using nanoparticles ofhydride-forming materials. Nanoparticles are defined in this inventionto include any condensed phase having an average equivalent diameterwithin about 2 to 200 nm (nanometers). This invention can includenanoparticles that are attached to each other to form essentially dryagglomerates while maintaining most of the surface area of thenanoparticles.

This invention improves hydrogen absorption and desorption rates, aswell as temperature and pressure relationships. Faster absorptiondecreases hydrogen loading/charging times. Faster desorption decreaseslag time. This is particularly important for automobile acceleration andfor the lag times characteristic for hydrogen reformers. If methane,gasoline, or some other fuel is reformed into hydrogen, a small fasthydride system like the present invention could be incorporated with alarger cheaper and slower hydrogen storage system. This combinationwould give better overall performance by ensuring a steady hydrogensupply to the fuel cell.

Hydride performance, and often storage, improves by decreasing thedistance hydrogen has to permeate into a hydride material. For example,hydrogen absorption/desorption rates and loading ratios improve withhigher hydrogen transfer rates. Many current systems achieve higherhydrogen transfer rates due to cracks that form in the hydridematerials. Nanoparticles offer the best possible ratio of surface areato volume. This is important in hydride-forming materials such as, butnot limited to FeTi alloys that bond hydrogen to their surface.Therefore, hydrogen transfer rates will be normally higher in nanophasehydride particles than in any other form of the same hydride. Onlychanges to the hydride-forming material's internal structure (e.g.,crystal structure) will cause deviations from this general trend.Smaller sizes should also reduce hydrogen release and uptaketemperatures and/or pressures for hydrides, and increase speed ofperformance.

This invention improves storage, by increasing catalytic sites andhydrogen to metal ratios, or by expanding the range of metals that canbe used. By packing in more hydrogen per weight of metal, hydrogenstorage density is improved. This enables a practical way of storinghydrogen onboard vehicles or at its other possible points of end use,and its more efficient generation at stationary sites, including larger,more efficient remotely located sites.

By having a very large surface area, nanoparticles offer fantasticsurface chemistry. Hydrides systems based on nanoparticles can store asignificant amount of hydrogen on surface sites in addition to itsstorage in interstitial sites (e.g. in palladium). The small particlesizes can increase storage density. Nanoparticles can be coated toenhance this surface chemistry. For example, nanomaterials could becoated or partially coated by gas or liquid phase processes during theformation of the nanomaterial. Dry coatings such as, but not limited toalkyl silanes and alkyl thiols can also help reduce powder loss orpowder blow out during use.

Nanoparticles should also increase the number of catalytic sites in thehydride storage system. This should allow the use of both amorphous andcrystalline materials with high storage densities. Small size can alsocreate catalytic activity not present in precursor or bulk versions ofthe same material.

This invention expands the range of materials that can be used toinclude cheaper or lighter materials, by improving various performancecharacteristics that had previously left such materials inadequate forpractical hydride storage usage. The nanoparticles of the presentinvention not only can increase kinetics and/or improve storage densitywith more catalytic sites, but can also allow uses of cheap and/or lightpreviously inefficient hydrides. Magnesium, nickel and iron alloys arenon-exclusive examples. Waste or cheap materials capable of partiallyforming hydrides such as some minimally processed ore, misch metals, orjunk ore could be used in situations such as stationary storage.

Materials that are now considered top candidates for hydrides, but whichhave nevertheless not yet reached the stage of broad commerciality,include magnesium hydride (MgH₂), magnesium-nickel hydride (Mg₂HiH₄),iron-titanium hydride (FeTiH_(1.95)), and lanthanum-pentanickel hydride(LaNi₅H₇). Nanophase versions of these and other metals, including thosecited previously, and alloys and/or compounds thereof, can both expandand improve the range of materials and operating and economiccharacteristics of the resulting hydrides, bringing them tocommerciality.

Palladium type metals form excellent hydride storage systems, but arevery expensive. Less expensive hydride systems suffer from lowerhydrogen loading ratios and lower hydrogen permeabilities. Nanophasehydride-forming materials allow using cheaper hydrides with lowerpermeabilities as well as giving better performance in expensivehydrides. Nanoparticles can be formed already in hydride form or in aform ready to adsorb hydrogen. For example, either palladium orpalladium hydride nanoparticles could be synthesized.

Reducing cracks can improve hydride characteristics in various ways.Cracks create less surface area than possible with nanoparticles.Minimizing cracking should decrease required volume of the storagesystem, and increase possible charging/discharging cycles. Minimizingcracking also prevents deformation or degradation of the hydridematerial. Due to their available high surface areas, nanoparticlesshould allow the use of more elastic hydride-forming materials that donot crack well. Nanoparticle size should also affect the temperature ofhydride formation and decomposition.

The nanoparticles typically have different properties than the precursorfrom which they were made, thereby broadening and improving the range ofpossible materials. This is largely due to their large surface area.Other reasons such as, but not limited to quantum effects andmorphological changes will also affect nanoparticle properties. Surfaceenrichment is also enhanced. Catalytic activity for hydrogen uptake andrelease is also enhanced. Nanoparticles can also change their form orshape more than larger particles. The small size could minimize crackingor deformation in metals that form flakes after absorbing hydrogen.

It is an object of this invention to create additional parameters fordesigning hydrogen storage systems. Nanoparticles' diameter, shape,crystalline structure, material, alloying, morphology, and otherintrinsic properties can be controlled, and can be combined with theselection of materials, mixtures, and alloys to drastically increase thepermutations and combinations of possible hydrogen storage systems. Theresult should enhance prospects for commerciality.

It is a further object of this invention to take advantage of thisseparate emerging new technology to create nanophase hydrides that canstore greater quantities of hydrogen, both by volume and by weight, thancan their precursor, standard hydrides; that can greatly broaden therange of available materials for hydrides; and that can improve oroptimize some or all of the various other hydride storage properties,such as, but not limited to materials costs, flow rates, speed ofresponse, pressure and temperature relationships, and various otheroperating characteristics of hydride storage systems.

Nanoparticle size ranges can be chosen based the type of material used,the surface area generated both by the size and the fabrication method,gas flow, powder flow, packing, and/or cost of manufacturing.Nanoparticles of different sizes and shapes can also be used together.

It is a further object of this invention to improve the space, weight,and/or safety of hydrogen storage and HFC systems. Space, weight, andsafety penalties are the biggest reasons hydrogen fuel is not already inwidespread use, whether in vehicles, stationary power, or portable powerapplications. The current invention aims at lessening these criticalnegatives. As another way of reducing weight and costs of hydrogen fuelsystems, this invention also allows the use of inexpensive and lightlow-pressure tanks; these are a major source of extra weight as well ascost in hydrogen gas or liquid storage systems.

It is a further object of this invention to improve the range ofmaterials available for hydrides. Certain materials that have a highability to store hydrogen by weight and volume, such as, but not limitedto magnesium hydride (MgH₂), may be inferior in some other operatingcharacteristics in the precursor form, but in nanophase form may haveequal or exceed alternative materials in these other operatingcharacteristics. The entire matrix of materials selection is thuschanged and broadened by the introduction of nanophase materials to themenu of materials to choose from.

It is a further object of this invention to improve operating andeconomic characteristics of hydride systems. The ability to customdesign nanophase grain diameter, shapes, and crystalline structure,together with the many combinations of materials, mixtures, and alloysof materials useful for hydrides, not only boosts hydrogen storagecapability by weight and volume density, but also greatly broadens theavailable range of materials and properties available. The resultpermits optimizing some or all of the various other hydride operatingand economic characteristics, such as, but not limited to materialscosts, flow rates, speed of response, pressure and temperaturerelationships, and various other operating characteristics of hydridestorage systems.

In this invention's preferred embodiment nanophase materials storehydrogen as a hydride Various combinations of nanophase diameters andnanophase materials or combinations of materials, including mixtures andalloys of materials with the same or different nanophase diameters, canbe designed to optimize at least many or combinations of the followingcharacteristics of hydride storage systems:

(a) Weight Density, i.e., the total weight of the hydrogen and hydridemetal in terms of deliverable energy stored. While the density ofhydrogen by volume in a conventional hydride is high, the density byweight is much lower because of the weight of the associated metal.Conventional hydrides at best are about four to five times heavier thangasoline because of the weight of the metals; the penalty would be stillgreater except that hydrogen alone has three times the energy density ofgasoline. Weight is especially important in the performance of anautomobile, or any other hydrogen transport system (e.g., transportationof hydrogen by truck). Nanophase metals for hydrides can substantiallyincrease the weight density of hydrogen storage.

(b) Volume Density, i.e., the total volume of hydrogen stored in avolume of hydride, in terms of deliverable energy content. At best, someconventional hydrides can store as much as a half the volume of hydrogenas the equivalent energy of gasoline. While this is up to twice theamount of hydrogen that can be stored in liquid form, and is about threetimes the hydrogen that can be stored as a gas at 5,000 psi, itnevertheless still represents a space penalty of at least twice that ofgasoline. The space requirement is especially critical in the design ofan automobile, or any other hydrogen transport system (e.g.,transportation of hydrogen by truck).

Nanophase materials for hydrides can increase the volume density ofhydrides in two ways: (a) storing a greater percent of hydrogen in themetal owing to the far greater surface area of the nanophase metalparticles; (b) engineering more volumetrically absorbing metal compoundsthat can store the hydrogen as a hydride. Optimal solutions for thesecharacteristics can be engineered owing to the different characteristicsof nanophase versus conventional materials, and the wider range ofmaterials available through different combinations of nanophasediameters and nanophase materials or combinations of materials.

(c) Materials Cost While nanophase hydrides entail greater cost ofmanufacture, their use broadens out the range of materials that can formhydrides, as well as the range of properties thereof, to permit bothless expensive precursor (parent) materials, and equal or more economicperformance characteristics from these materials, as listed in the otherparts of these claims. Either through the cheaper materials, theirgreater performance, or both, economics of hydride storage systems canbe improved. This and the other specific hydride performancecharacteristics can be optimized via the different characteristics ofnanophase versus conventional materials, and the wider range of hydridesavailable through different combinations of nanophase diameters andmaterials or combinations of materials. The current cost to makenanophase materials should decrease in the future. Also, nanoparticlescompare favorably to the high cost and limited availability ofpalladium.

(d) Flow Rates; i.e., the rates at which hydrogen discharges from thehydride when the heat of decomposition is applied. The flow rate ofrelease of the hydrogen benefits from the smaller particle sizes ofnanophase particles, giving more avenues for exit of the hydrogen gas.The speed of response upon reaching of the heat of decompositionlikewise benefits for the same reasons. The heat of decomposition is theheat required to begin releasing the hydrogen as a gas.

(e) Speed of Response; i.e., the speed at which hydrogen gas begins toflow upon reaching the heat of decomposition. The speed of response,i.e., quicker thermodynamics, is critical to a smoothly functioningvehicle power system. This and other specific hydride performancecharacteristics can be optimized via the different characteristics ofnanophase versus conventional materials and the wider range of materialsavailable through different combinations of nanophase diameters andmaterials or combinations of materials.

(f) Plateau Pressure; i.e., the flattish region of the S-shaped curve ofvolume of hydrogen absorbed in the hydride versus pressure (at aconstant temperature). This is the region in which most of the hydrogenis absorbed with little pressure change. This S-shaped curve of hydrogenabsorption versus pressure, plotted at a constant temperature, is knownas an isotherm, an example of which is depicted in FIG. 1; at highertemperatures, approximately the same curve shifts higher. Plateaupressure for a given temperature can be engineered in conventionalhydrides by the selection of metals, alloys, and intermetalliccompounds; with nanophase materials the plateau pressure can be furthertailor-designed by the choice, mixtures, and alloys of materials and canbe supplemented with different nanophase diameters of same.

(g) Plateau Pressure-Temperature Relationship; i.e., the temperature atwhich isotherm pressure plateaus occur. The temperatures can be raisedor lowered by the choice of materials in conventional hydrides,sometimes at the compromise of other properties such as, but not limitedto volume. Further ranges of flexibility can be obtained with nanophasematerials with the selection of nanophase diameters, eliminating orreducing any compromises of other properties. This invention can reduceexternal energy (e.g., waste heat) required for hydrogen desorption fromhydrides.

(h) Plateau Slope; i.e., the (usually modestly rising) slope of theplateau region of the above curve, or isotherm. This can be flattened inconventional hydrides with the appropriate annealing treatments prior tocrushing and activation. Many nanophase hydrides should not need thisactivation step. A surface or sublayer can be added to the nanoparticleto replace or minimize activation. The same effect can be accomplishedwith nanophase size particles, and the choice of nanophase diameters andmaterials combinations can further aid in designing the plateau slope. Aseparate annealing step should not be needed for nanoparticles.

(i) Hysteresis; i.e., the pressure difference between absorption anddesorption isotherms, or the difference in pressure to absorb versus todesorb hydrogen from a hydride. This asymmetry varies between alloys andmust be taken into account in designing a system, especially whendifferent hydride beds are to be coupled in closed cycle operation. Dualbed or multiple bed systems can combine characteristics of specifichydrides for more economical or efficient overall system. A hybridstorage system is envisioned as part of this invention. A nanophasecomponent could be used for quick response in combination with acomponent of partly larger particles for potentially higher storagedensity with a slower response (dual bed, see Daimler-Benz in Sci.Amer., p. 7). Nanophase hydrides with their greater combination ofdiameters and materials can further tailor-design the hysteresis of ahydride.

(j) Ease of Activation; i.e., of hydriding the alloy for the first time.Some alloys can be activated quite easily even at ambient temperature;others are difficult to activate apparently because of a surface barrierthat must first be eliminated. Nanophase materials may directly addressthe latter problem, but in addition afford a broader range of materialsfor hydrides, and nanophase diameters of same, thus giving greaterflexibility for dealing with ease of activation.

(k) Withstanding Poisoning, or Deactivation, with Impure Gas Streams;e.g. from air, carbon monoxide, and sulfur dioxide. Different compoundshave different degrees of tolerance for such. Nanophase materials, bygiving greater combinations of diameters and materials, can furthertailor-engineer to minimize this problem, boosting the flexibility andperformance of the hydride.

The nanoparticles of the present invention could be used as a getter toclean hydrogen or other fuels before or during use in fuel storage,reforming to hydrogen, or in HFCs themselves, to minimize poisoning ofhydride-forming materials, catalysts, or electrodes . Catalysts arefound in storage, reformers, and electrodes. A mixture of nanoparticlescould include hydrides and getters. Alternatively, a small exchangeableand/or regenerable cartridge of nanoparticles could effectively removepoisons from hydrogen, gasoline, methanol, other fuel, or air. Forexample, oxygen can be getted to increase hydrogen storage levels, andplatinum-ruthenium alloy catalyst can be used to prevent poisoning inmethanol converters.

(l) Longer Cycle Life; i.e., ability to absorb and desorb the samequantity of hydrogen many times without deterioration.

(m) Other Characteristics. Other properties and characteristics whichare taken into account in conventional hydrides can be furthertailor-engineered with nanophase hydrides, given their greatercombinations of diameters and materials to choose from.

Any nanoparticle fabrication processes that can be cost-effective formass production are envisioned. Some representative examples follow.This invention envisions creating hydrogen-storing nanoparticles usingany of the many nanofabrication techniques that are being found now andin the future. Representative examples include:

Flame reactors typically form oxides and chlorides that could beprecursors for hydrogen storage materials. Spray roasting and hot wallcould be examples.

Combustion synthesis uses an oxidizer (e.g., metal salts) and a fuel(e.g., organic compounds) in a redox reaction. This method createsloosely agglomerated nanoparticles with a high production rate and cheapraw materials.

Evaporation/condensation (EC) generators have a low production rate dueto low operating pressures (usually a few Torr), but potentially couldbe scaled up like aluminized Mylar sputtering applications were.

Spray pyrolysis, plasma processing and powder spray could be used inconjunction with a supersonic nozzle.

Liquid phase methods could use solution chemistry such as supercriticalfluids, chemical reduction, or chemical oxidation.

Mechanical alloying for hydrides is not considered as part of thisinvention unless it is used in combination with another process. Ballmilling and other mechanical alloying predominantly create aggregateslarger than the nanoparticles of this invention.

Template methods form nanoparticles within small voids or areas.Zeolites, pillared clays, nanoporous membranes and inverse micelles(e.g., water in oil) are non-exclusive examples.

Prior work in this field used very expensive and slow procedures and notof interest in this invention, which seeks to provide lower cost,potentially commercial hydrides. Prior work using the term “nano” seemto be larger particles with nanostructured features such as crystalsize.

The nanoparticles and ultrafine powders of the present invention may besubject to many different names and definitions since we are still inthe early development of nanotechnology. This invention uses thefollowing definitions.

This invention uses particles with many different shapes. Some genericexamples include spheres, hollow spheres, flakes, whiskers, isolatedcrystals, etc. The size of these particles are usually measured asequivalent spherical diameters. That is the diameter of a sphere withthe same volume as the particle in question. This invention usesparticles with equivalent spherical diameters of about 2-200 nm. Wedefine these particles as nanoparticles.

Nanoparticles often attach to one another by at least one of severalmechanisms. Nanoparticles can be physically attached to form a largeaggregate or bulk material. Aggregates are usually not of nanometerscale, but can be made of what were originally nanoparticles fused toone another. For example, normal sintering can fuse the originalnanoparticles. Aerogels are very low density aggregates ofnanoparticles. Bulk materials can be made up of nanocrystallites. Theseaggregates and bulk crystallite materials may have originated fromnanoparticles, but are not part of the present invention.

This invention does include agglomerates which are nanoparticles thatare only held together by van der Waals forces and other surface forcesof attraction, and includes other essentially dry agglomerates ofnanoparticles. The invention also includes light sintering or pressingwhile preserving at least 50%, but preferably at least 75%, of thesurface area of the nanoparticles. Unlike aggregates, agglomerates canbe broken apart mechanically and/or by colloidal suspension, often butnot exclusively into their separate nanoparticle sizes.

This invention can include nanoparticles that are attached to each otherto form a larger structure while maintaining most of the surface area ofthe nanoparticles. Representative examples include nanoparticlesincorporated into and/or on a hydrogen permeable and/or porous membrane.

The nanoparticles of this invention must be carefully held to avoidlosing the very fine powder. However, it is known that these particlesmay loosely bind or agglomerate together because of their large surfacearea. This method could provide the greatest storage and storage densityat the lowest cost. In addition, the nanoparticles can be bound to eachother (e.g., by a binder), a membrane, other substrate, or be held by anat least partially hydrogen permeable container. For example, a spiralwound Pd-coated sheet of cheaper hydriding material could be used insidea tank. The sheet could be hydrogen permeable or selectively hydrogenpermeable, the latter keeping out or getting poisons or impurities. Inanother example, a rigid tank with an internal flexible bladder couldhold a hydride and hydrogen separated from methane with a selectivelyhydrogen permeable bladder. Alternatively, gasoline could be separatedfrom the hydride/hydrogen. Packing of particles will affect the cycletime and efficiency.

Fluid beds are also envisioned. The nanoparticles could be agitated in afluid bed during hydrogen charging, or for longer times. For example,agitation could be provided by a vehicle's drive train or shocks.

This nanoparticles of the present invention can be lightly pressed andor sintered into shapes if the majority of the nanoparticles' surfacearea remains. This could reduce motion and loss of the nanoparticles.

Mixtures of different hydrides is also envisioned. Different materials,hydride forms, crystal structures, sizes, and shapes are envisioned. Forexample, carbon monoxide and sulfide scavengers could be mixed withhydride storage nanoparticles or could be used as a prefilter at anypoint along the production, storage, distribution, and use. Examplesinclude but are not limited to removing sulphur from gasoline beforereforming, removing sulphur from hydrogen before filling a hydride tank,and removing oxygen at the inlet to a fuel cell. Mixed fuel storage isenvisioned. Separation of fuels, such as, but not limited to hydrogenfrom methane in a gas well is also envisioned.

Non-hydride nanoparticles could also be mixed with the hydride-formingnanoparticles. Some reasons for these mixtures can include enhancingthermal properties, acting as poison getters, improving flowcharacteristics, binding particles to minimize their loss with gas flow,catalysis, and/or creating channels for gas flow. Some examples ofnon-hydride nanoparticles include silica sol, ceramic nanoparticles,semiconductor nanoparticles, and/or light sensitive materials.Nanoparticles with different hydride-formation properties can also bemixed together.

Nanoparticles of the present invention can also be mixed withconventional macro-sized hydrides to improve catalysis or modify thehysteresis curve.

Esoteric materials such as, but not limited to mischmetal alloys, junkore, precursor metal mixtures recovered from ore, polyhydride complexesusing cobalt or other transition materials, and organosilicones areenvisioned components of the nanoparticles of the present invention.Polyhydrides can usually store more hydrogen monohydrides. Manycatalysts (e.g., palladium) that bind hydrogen can also be used forstorage or to coat hydride particles to improve storage kinetics andcapacity.

Hydrogen can be released from the nanoparticles by changes intemperature, electricity, magnetism, pressure, chemicals,electrochemistry, pH, volume (e.g., injection into an ICE), etc.Parameters will often be different than in the conventional bulk hydridesystems.

The nanoparticle surface can be altered to affect surface poisoning.Generally, surface poisoning is a problem in hydride storage. Carbonmonoxide and sulfur compounds are common problems in palladium typesystems. Due to its high surface area, the nanoparticle in thisinvention should be protected from poisoning gases. Alternatively, thenanoparticle's contents or at least surface can be selected to beresistant to poisoning during use in its intended application.

Buildup of surface coatings such as, but not limited to oxides canreduce hydrogen permeation. Due to their high surface area, thenanoparticles in this invention must be designed to have minimal surfacebarriers. For example, the particles could be kept in an inertatmosphere. Or heating nanoparticles and/or nanoparticle hydrides inpure hydrogen can remove oxide surface layers. Nanoparticles can also becoated to minimize oxidation. Preferably oxide regrowth is preventedbefore coating.

The nanoparticles can be porous to further enhance surface area.However, too much porosity will reduce storage density especially whenhydrogen is mainly stored in the bulk of the nanoparticle.

The nanoparticles can be virtually pure, alloys, coated particles,multilayer particles, or mineral combinations.

In the present invention, hydrogen, other fuels, or liquids can bestored in the spaces between the particles (compared to the interstitialsites of hydrides), for applications including but not limited tostorage, blending gases, safety, or getter applications. The surface ofthe nanoparticles can interact with the stored material. The storedmaterial can be held by capillary action, hydrogen bonding, and otherchemical bonding and physical interactions. For example, a mixture ofsolid hydride nanoparticles can be mixed with a liquid such as, but notlimited to gasoline or methanol. Adding 5% hydrogen to gasolinedecreases NO_(x) emission by 30-40%. Hydride nanoparticles can be mixedwith other materials to provide a hydrogen mixed with other gasses orvapors upon request. Non-hydride nanoparticles (e.g., polymeric) can bemixed with volatile liquids to reduce evaporation rate, therebyminimizing explosion and flammability risks.

Condensation in capillary inter-particle spaces between nanoparticlesallows fast hydrogen permeation. These spaces could also storecondensable gases as an additional storage mechanism.

Methane can be reacted with nanoparticles, such as in a metal carbidesystem, to provide a safe way of storing natural gas and other lowdensity hydrocarbons. Storing other low density fuels in similar ways,including but hot limited to propane, butane, ethane, natural gasoline,and LNG, are also envisioned.

Additives can be added to the hydrogen either in storage or from othersources to improve storage, fuel cell performance, emissions, etc. Thenanoparticles could be designed to be compatible with such systems.

Alternatively, nanodroplets of or containing liquid hydrides or hydrideprecursors could be used for storage of chemical hydrides. For example,nanodroplets of decaline or methyl cyclohexane with or without aseparate catalyst are envisioned. The catalyst could be incorporated inthe nanodroplet or may not be needed due to the nanodroplet size. Thenanodroplets could be created before distribution in the infrastructuresystem or could be created in situ in a vehicle just prior to burning inan ICE, or other oxidation such as a fuel cell. Explosive parameterssuch as, but not limited to carbon content would dictate whichcombinations would be safe. Solid chemical hydride nanoparticles, suchas sodium aluminum hydride or calcium hydride, are also envisioned.

Application of this invention include the following. Storage ispermitted throughout the hydrogen usage system. Hydrogen can be storedin nanophase hydrides as a means of on-board vehicle storage forvehicles powered by a hydrogen fuel cell, or as a means of storinghydrogen at service stations, garages, central fleet refueling stations,even individuals' homes, or other points of use, before use by vehicles.The source of such hydrogen could be on-site generation, either byelectrolysis or by steam methane reforming; or alternatively, off-sitegeneration, delivered by truck or pipeline; or even produced inindividuals' homes or other points of use, where the safety of hydridestorage could permit hydrogen generation. Minimizing weight andespecially volume are major requirements for non-stationaryapplications.

For any of these sources of generation, more flexible and/or economichydrogen generation is permitted. The hydrogen can be stored innanophase hydrides, thus permitting capturing the economies of eithercontinuous around-the-clock generation for steam methane reforming, orof off-hours evening generation when electric rates are lower forelectrolysis.

Nanophase hydride storage can permit transportation of hydrogen toservice stations or other distribution points from remotely locatedlarge steam methane reforming hydrogen production systems. These wouldbe cheaper due to economies of scale, and more environmentally friendlysince they reduce to nearly zero the local, urban-area smog pollution ofHFCs in urban areas, where smog is a problem.

Hydrogen can be stored in nanophase hydrides and transported in trucksor rail to market for tapping renewable and zero-pollution hydrogenenergy supplies, which are typically remote from the points of use, suchas, but not limited to biomass, municipal waste, or electrolysis ofwater using solar, (PV or solar-thermal-electric), wind, or hydroelectricity. Hydrogen can be stored in nanophase hydrides andtransported in trucks or rail to market for harnessing currentlyexperimental hydrogen production techniques, among them beingphotobiological processes, photoelectrochemical processes,thermochemical processes, and radiolysis.

For onboard vehicle use, hydrogen can be stored in nanophase hydrides invehicles fueled with methanol or gasoline with onboard hydrogen reformersystems, which have some speed of delivery problems. In this applicationhydrides, using nanophase materials, can store excess hydrogen at stoplights or other stops and deliver this excess in the first seconds ofacceleration, taking out the delays of response of the on-board reformersystems.

For distribution, hydrogen can be stored in nanophase hydrides in bulkstorage, required in large scale hydrogen distribution systems toprovide a buffer between production facilities and fluctuations indemand.

For non-vehicular uses, hydrogen can be stored in -nanophase hydridesfor storage, transportation, and use in stationary power hydrogen fuelcell systems, whether using PEM or other fuel cell systems. Hydrogen canbe stored in nanophase hydrides as a means of storing, transporting, andusing hydrogen safely, conveniently, and economically for residential,commercial and industrial uses, and for transporting it to these pointsof use. Storage and transportation of hydrogen in nanophase hydrides canbe used for storage, transportation, battery replacement, and use infuel cells for portable power products (e.g., laptop computers, mobilephones, or other portable appliances) and portable fuel celldemonstration systems for marketing or educational purposes.

Nanophase hydrides can store hydrogen for storage, transportation, anduse in: hydrogen-burning appliances (such as, but not limited to ovens,ranges, barbecue grills, fireplace “logs,” hydrogen-fired clothesdryers); hydrogen-fueled internal combustion engines; marineapplications, including ship propulsion and on-board electricitygeneration; and aviation or space applications, utilizing the lighterweight, lesser volume, and greater safety characteristics of nanophasehydrides.

Nanophase hydrides can be used in chemical and industrial industries andthese industries' applications (e.g., production of ammonia, refining ofpetroleum products, production of methanol and other chemicals, for foodhydrogenation, ironmaking of steel and glass, and in the electronicsindustry), giving greater flexibility than at present, in whichhydrogen's use must typically now be geared more closely to itsproduction than would be required with a more economical and effectivestorage and transportation system via nanophase hydrides.

Nanophase hydrides can store and transport hydrogen from cleanup ofindustrial off-gasses, which hydrogen is now used principally on-site bythe industry that produces it, but might more valuably be used in othermarkets given an economic and effective storage and transportationsystem via nanophase hydrides.

This invention can eliminate or reduce the need for electricaltransmission systems in developing countries by converting electricityto hydrogen at the point of generation, and storing and transporting thehydrogen to the point of end use via nanophase hydride transported bytrucks, trains, or other existing infrastructure. The same applicationcould apply in new or replacement energy transportation systems indeveloped nations.

Applications of this invention are also envisioned to include any otherapplications in which hydrogen is stored or transported, hydrogenpurification, hydrogen recovery, ethane recovery, natural gas recovery,hydrogen separation, thermal compression, chemical heat pumps,refrigeration without CFCs, deuterium and/or tritium enrichment, andenergetics.

These advantages made possible by this invention should greatlyfacilitate and accelerate the adoption of hydrogen for fueling vehicles,whether via HFCs or hydrogen ICE designs, by making possible morecompact, safe, lower-cost, lower-weight on-board hydrogen storage.Likewise, the same advantages should similarly greatly facilitate boththe transportation and end-point distribution of hydrogen, as well asstorage following generation, further facilitating and accelerating theadoption of hydrogen for vehicles. The same advantages should likewiseapply to HFCs for stationary power use and associated hydrogen storageprior to use, storage during transportation and distribution, andstorage following generation. These same advantages should likewiseaccrue to HFCs for portable power products.

This invention should help provide such a more economic means oftransportation and distribution of remotely generated hydrogen. It wouldoffer a transportation method similar to that of tank trucks forgasoline or heating oil, but more economic than would now be possiblevia trucking liquid hydrogen or compressed gas hydrogen.

An example would be to store and/or transport liquid hydrogen moresafely by slowing gasification of the hydrogen. Hydrogen would be storedas a hydride in the nanoparticles and on the surface of thenanoparticles. Hydrogen would also be stored as a liquid between theparticles and held by capillary action, etc. This liquid hydrogenbetween the particles should behave differently than bulk liquidhydrogen because of its interaction with the close surfaces of thenanoparticles. Potentially, higher temperatures and/or lessrefrigeration may be possible. Another example would be to store and/ortransport liquid natural gas (LNG) in and between absorbent polymernanoparticles. This would slow the rate of release of gaseous naturalgas during tank leakage or rupture. Slowing release of these gasesshould minimize explosions, freezing and asphyxiation dangers. Theseexamples also should allow less stringent refrigeration and storagevessels.

Since there are emission benefits to be derived from hydrogen additivesversus pure gasoline, a more practical alternative would be mixing up toperhaps 20% compressed hydrogen with gasoline in the carburetor orengine itself. For any of these possible hydrogen ICE applications amethod would still be required for hydrogen storage, both onboard thevehicle and prior to its use. Hydrogen could be mixed with oxygen withinnarrow safe ratios. Hydrogen could be mixed with water to improve ICEperformance. Safety concerns have to be addressed when mixing hydrogenwith carbon or oxygen.

This invention includes the following materials, systems, and uses. Amaterial for storing hydrogen as a hydride, wherein the materialcomprises a non-graphitic nanoparticle capable of storing hydrogen as ahydride, adsorbed hydrogen, or combination thereof, said nanoparticlehaving an average diameter of about 2 nanometers to about 200nanometers. A material for storing hydrogen as a hydride, wherein thematerial comprises a mixture of particles capable of storing hydrogen asa hydride, wherein essentially all of the particles have at least twodimensions of at least about 2 nanometer and no more than about 200nanometers. A material for storing hydrogen as a hydride, wherein thematerial comprises a mixture of nanophase particles, with an averagediameter of 2 to 100 nanometers. A material for storing hydrogen as ahydride, wherein the material comprises a mixture of nanophaseparticles, with an average diameter of 100 to 200 nanometers. A materialfor storing hydrogen as a hydride, wherein the material comprises amixture of nanophase particles, with an average critical dimension of 2to 80 nanometers. A material for storing hydrogen as a hydride, whereinthe material comprises an aggregate of nanomaterials, wherein theaggregate has an average critical dimension of 15 to 200 nanometers. Ahydrogen storage material, which comprises a non-graphitic nanomaterialwith a critical dimension less than 40 nanometers. A hydride, whichcomprises a nanomaterial with a critical dimension less than 100nanometers. A hydrogen storage material, which comprises a materialaccording to claim 1 and a second material having all of its dimensionsgreater than about 200 nanometers, said second material being at leastone member selected from the group consisting of a hydride-formingmaterial, a hydrogen adsorbing material, a support, and an additive toenhance performance of the hydrogen storage system. A material forstoring hydrogen as a hydride, wherein the material comprises ananoparticle capable of storing hydrogen as a hydride, said nanoparticlehaving an average diameter of about 200 nanometer to about 950nanometers.

The materials of this invention can catalyzes the splitting of molecularhydrogen to atomic hydrogen, can be a dry metal, can be coated (e.g., bya oxide or poison resistant coating), and can be on a support (e.g.,membrane, sponge, etc.). The materials of this invention have at leasttwo different sizes or can be a mixture of at least two differentnanoparticles made of different materials. The materials of thisinvention can comprises an alloy, junk ore or a precursor metal mixturesrecovered from ore. The materials of this invention can comprises aliquid nanodroplet of a chemical hydride.

The materials of this invention can be in a gas, in a vacuum, or in aliquid. The nanoparticles of this invention can be crystalline and/oramorphous.

The materials of this invention can be used in storage systemscomprising any of the following: the material of claim 1 in a firstcontainer, and a slower and cheaper hydrogen storage system in a secondcontainer; a support for holding the material while allowing flow of ahydrogen gas and a low pressure hydrogen storage container to hold thesupport and the hydrogen gas; a fluid bed; and/or a filter bag. Thematerials of this invention can be pressed, sintered, or pressed andsintered into a form with an average minimum dimension of greater thanabout 1 millimeter, wherein the surface area of the form is at least 50%of the surface area of the nanoparticles.

This invention includes hydrogen storage systems for use with a portablefuel cell, vehicles, transportation, distribution, stationary fuelcells, point-of-generation storage., and to average out periodicallyavailable power sources. The materials of this invention can storehydrogen in the presence of an additional gas or vapor and optionallyseparate at least some hydrogen from a gas mixture.

The materials of this invention can be used for the following methods:using a macrosized hydride by at least partially replacing themacrosized hydride with the nanoparticles according to claim 1, whereinthe macrosized hydride and the nanoparticles differ only in size andmorphology; to minimize time lags in delivering hydrogen from onboardreformers.

Some of the materials of this invention can be used as a poison getter,comprising a material capable of separating a poison from an impurehydrogen gas or an impure fuel convertible into hydrogen by a reformer,wherein the poison reduces hydrogen storage capability of a hydrogenstorage system or reduces efficiency of the reformer; wherein thematerial comprises a mixture of non-graphitic nanoparticles capable ofadsorbing the poison but not absorbing the hydrogen gas or the fuel,wherein the nanoparticles have an average size of about 2 nanometers toabout 200 nanometers; and wherein the material can be removed from thehydrogen storage system or regenerated to remove the poison by heatingor chemical treatment.

Some of the materials of this invention can be used for storing andreducing evaporation rates of at least one member selected from thegroup consisting of methane, ethane, propane and natural gas, whereinthe material comprises a mixture of nanophase particles, with an averagediameter of 2 to 200 nanometers.

The following example will serve to further typify the nature of thisinvention but should not be construed as a limitation in the scopethereof, which scope is defined solely by the appended claim.

EXAMPLE 1 Hydrogen Storage Using Palladium Nanophase Particles

One kilogram of 30 nm palladium nanoparticles is placed in a lowpressure container with an aperture for hydrogen gas input and output. Aheating coil is wrapped around the container for hydrogen release. Thenanoparticles are wrapped in a spiral wound hydrogen permeable membraneto avoid particle blow out.

EXAMPLE 2 Hydrogen Storage Using Inexpensive Nanophase Particles

One kilogram of iron nanoparticles with average diameters of 50 nm areheld within a hydrogen permeable bag. The bag is expandable to containthe nanoparticles even if the volume within the bag quickly changes. Thebag may have pores smaller than 40 nm. The bag is held within a lowpressure vessel that is resistant to hydrogen embrittlement and capableof being gently heated and optionally cooled for hydrogenrelease/uptake.

EXAMPLE 3 Hydrogen Storage for Portable Devices

A metal cylinder, with a 4 cm inner diameter, a pressure release valve,and an openable gas-tight outlet is filled with a mixture ofnanoparticles. Over 99% of the nanoparticles are FeTi. Under 1% of thenanoparticles are palladium. The nanoparticles are not perfectlyspherical, but have an average equivalent spherical diameter of 50 nm.At least 96% of the nanoparticles have equivalent spherical diametersbetween 10 nm and 100 nm. Many of the nanoparticles may sometimes beheld together by van der Waals forces or other forces of surfaceattraction. The nanoparticle mixture is placed in sintered metal tubes.The tubes are placed in the cylinder. The metal tubes are permeable tohydrogen, but hold the nanopowder. The nanoparticles are partially heldin place by caking and otherwise clogging the pores in the sinteredtubes. The metal cylinder is connected to a fuel cell through aminiaturized pressure regulator.

EXAMPLE 4 Method of Making Inexpensive Nanoparticles

Molten magnesium is sprayed though a supersonic nozzle, through a cooled150 mTorr hydrogen atmosphere, and onto a −77° C. flexible belt. Thebelt continuously passes through liquid nitrogen, passes through thespray, and then removes deposits by sharp bends and/or knife scrapping.Magnesium and/or magnesium hydride nanoparticles are separated from thebelt. A cost effective average equivalent spherical diameter of thenanoparticles is 100 nm. Reducing the pressure of the hydrogen reducesthe nanoparticle size and the magnesium to magnesium hydride ratio. Thenanoparticles are kept in a hydrogen or inert atmosphere to avoidpoisoning or deactivation.

EXAMPLE 5 Method of Making Inexpensive Hydride Storage System

Molten magnesium is sprayed though a supersonic nozzle, through a cooled150 mTorr hydrogen atmosphere, and onto a polymer film. The polymer filmis cooled, but above its glass transition temperature. The polymer filmis very permeable to hydrogen and/or is porous. The polymer film ismoved past the spray quickly enough to keep the spray coating thinenough to maintain flexibility. The spray coated film is wound in aspiral configuration and placed in a metal or reinforced polymercomposite outer container. The container can be disposable,rechargeable, or recyclable.

We claim:
 1. A material for storing hydrogen as a hydride, wherein thematerial comprises: an aggregate of nanomaterials, wherein the aggregatehas an average critical dimension of 15 to 200 nanometers.
 2. A materialfor storing hydrogen as a hydride, wherein the material comprises: amixture of nanoparticles capable of storing hydrogen as a hydride,wherein essentially all of the particles have at least two dimensions ofat least about 2 nanometer and no more than about 200 nanometers,wherein the nanoparticle is in a liquid.
 3. A method of using a materialfor storing hydrogen as a hydride, comprising: (1) contacting thematerial with hydrogen in the presence of an additional gas or vapor,wherein the material comprises a mixture of nanoparticles, whereinessentially all of the particles have at least two dimensions of atleast about 2 nanometer and no more than about 200 nanometers so that atleast part of the material reacts with the hydrogen to form a hydride;and (2) heating the hydride to release at least some of the hydrogenfrom the hydride.